The initial objectives of this project were to use human adenoviruses and adenovirus - SV40(Ad2-240) recombinants as tools to study the genetics of DNA tumor viruses, to define the role of viral genes and viral antigens in viral oncogenesis and to study the biology of Ad2-SV40 recombinants. Due to the lack of proper containment facilities in NIAID between January 1973 and May 1978, there has been a 5-year disruption (see past reports) in the major thrust of this project. During this interval, a study of Ad2-SV40 recombinants associated tumor induction by these agents with the incorporation into the adenovirus - 2 chromosome of a specific segment of SV40 DNA. To begin to understand the mechanism by which this SV40 DNA segment conveys oncogenicity to these recombinants, it was necessary to understand why Ad2 was nononcogenic for hamsters. Since Ad2 will transform hamster cells in tissue culture, we initiated a study of the oncogenic properties of Ad2 transformed cells. The results thus far lead us to suspect that unrecognized host immune mechanisms in the hamster reject Ad2 transformed cells and transformed cell-induced tumors. Such a concept suggests that the presence of a specific segment of the SV40 genome might induce functions in hamster tumor cells that interfere with the rejection process. Future studies will be directed toward more carefully defining these concepts.